High Dynamic Range (HDR) is a new technology being introduced by a number of standard organizations (e.g., Blu-ray Disc Association, ISO/IEC HEVC, ITU-R, SMPTE, CEA, and HDMI) and private companies (e.g., Dolby, Philips). New devices such as UHD Blu-ray disc players and UHD TVs are expected to support HDR technologies in the near future, starting in 2015. Blu-ray Disc Association (BDA) has completed its Version 3.0 draft specification document on the new UHD (Ultra High-Definition) Blu-ray™ disc standard that includes HDR and WCG (Wide Color Gamut) in April 2015. Video streaming service providers such as Netflix, Amazon, and Vudu are working on HDR video streaming service specification as of now and are expected to start UHD HDR video streaming services this year. Other international standard organizations such as ITU-T, ITU-R, ISO/IEC, SMPTE, and HDMI are working on the next generation standards and solutions to support HDR videos.
HDR has been a relatively familiar topic in digital photography, but its concept and methodology is different from what is being referred to herein. HDR in digital photography refers to combining multiple low dynamic range (or standard dynamic range) images of the same scene captured at different exposure levels into a single high dynamic range image. HDR, as referred to herein, instead refers to a new video processing pipeline that captures, compresses, pre- and post-processes, and displays pictures at a much higher dynamic range than previously allowed by the existing devices.
The requirements to playback High Dynamic Range (HDR) videos include two main use case scenarios.                1) Playback of HDR videos on HDR display monitors or TVs        2) Playback of HDR videos on legacy Standard Dynamic Range (SDR) display monitors or TVs        
The second use case requires converting the High Dynamic Range (HDR) videos to Standard Dynamic Range (SDR) videos. This is a mandatory part of the new BDA UHD Blu-ray specification. This conversion from HDR to SDR is also expected as a key technology in the next years while the new HDR-capable display monitors and TVs start penetrating the mainstream consumer market in the US and the rest of the world, along with the HDR video contents from Blu-ray discs, streaming services, and personal recordings of end users.
Based on the information available as of today, the HDR video format is defined by HEVC Main10 High Tier Level 5.1, BT2020 color space, SMPTE ST2084 EOTF, and SMPTE ST2086 static metadata.
Considering that the existing SDR video format is defined by Rec709 color space, Rec709 OETF, and Rec1886 EOTF, the HDR to SDR tone mapping requires conversion between BT2020/Rec709 color spaces and gamma correction using ST2084/Rec709 EOTF/OETF.
The new SMPTE ST2084 EOTF covers the dynamic range up to 10,000 cd/m2 (or nits) whereas the existing Standard Dynamic Range (SDR) Rec709 OETF covers a much smaller dynamic range in [0, 100] nits.
Accordingly, without the proper method applied to convert High Dynamic Range (HDR) to Standard Dynamic Range (SDR), the HDR content displayed directly on the SDR monitor/TV will be in incorrect brightness/contrast/color and unsuitable for viewing.